There is known a shipbuilding complex to build tankers, bulk and ore carriers and combination bulk carriers (cf. Navires, ports et chantlers, 1969, No. 226, pp. 197-200). Vessels constructed at such a shipbuilding complex are of the type that comprises an aft end, a parallel middlebody and a fore end.
The prior-art shipbuilding complex comprises a dry dock with a dock adjacent area, and a flooding chamber adjacent to the head of the dry dock. The flooding chamber must be long enough to make room for two assembly stations: the aft end is assembled at the head of the flooding chamber, whereas hull parts without the fore end are assembled in the area of the flooding chamber adjacent to the dry dock.
The shipbuilding complex under review operates as follows.
After a completed ship is floated from the dry dock, the water level therein is raised to a level high enough to flood the flooding chamber so as to set afloat the hull parts found there at the moment. The hull without the fore end is transferred to the dry dock; the aft end is moved to that part of the flooding chamber which is next to the dry dock. The flooding chamber and dry dock are then emptied so that the hull components are placed on their floors. The dry dock is used to complete the hull without the fore end and at the same time assemble the fore end; the flooding chamber is used to add the parallel middlebody to the aft end; the vacant assembly station at the head of the flooding chamber is used to assemble the aft end of another vessel.
The foregoing shipbuilding method is such that the overall dock length must be at least 900 to 1,000 meters; clearly, it takes such money and effort to build a structure of that size.
The absence of an intermediate gate in the dry dock makes it impossible to use the progressive flow-position assembly method. According to this method, individual hull components are successively brought to the dry dock to be joined together; this method makes it possible to substantially reduce the length (and, conequently, the cost) of the flooding chamber and curtail the slipway period of construction, because a considerable share of assembly operations is carried out in closed erection shops.
There are known a number of methods for building gas carriers which have a fore end, a parallel middlebody accommodating tanks for liquefied gas, and on aft end.
One of such methods is described in "Zosen", 1976, vol. XX, No. 11, and in "Kawaski Topics", August 1977, No. 67.
According to this method, the hull is built in a dock, whereas the tanks are built in a closed shop. Conventional cranes are used to install the tanks in the hull.
The tanks of modern gas carriers are very heavy and have to be lifted by cranes whose capacity, as a rule, is higher than that of a crane that would be used to build a vessel's hull along. High-capacity cranes are quite expensive.
There is further known a method for building liquefied gas carriers without using cranes in the course of the construction (of. French Pat. No. 2,158,851, Cl. B63b, 9/00, of 1973).
According to this method, the hull and tanks are assembled in an H-shaped dock. One chamber of the dock is used to assemble the hull; liquefied gas tanks are assembled in the second chamber which is parallel to the first. The sizes of the two chambers are about equal.
Through the transverse chamber, completed tanks are transferred to the chamber accommodating the hull which at this stage is composed of a fore end and aft end spaced at a distance which is greater than the length of the tanks. The tanks are installed afloat after the H-shaped dock is flooded, hull parts are set afloat.
The flooding of the dock accommodating a hull under construction accounts for a relatively long time on the stocks of construction. The method under review is also disadvantageous in that it requires a costly second dock chamber for the assembly of tanks.
According to this method, the tanks can be installed in the hull only by using high-capacity cranes or by flooding the dry dock and setting the gas carrier's hull afloat.